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<br />-------...:...- <br /> <br />O~~ '''':''~ <br />tJ " 11;) u <br /> <br />Theoretically, it would now have been possible to compute the average <br />annual natural salt loading if the average monthly natural flows were <br />known. It was felt, however, that the relationships were not strong <br />enough to provide this value with any reliability. Therefore, the <br />results from the procedure described above were used to provide a <br />means for distributing on a monthly basis independent estimates of <br />annual natural and man-caused salinity values. The independent esti- <br />mates used were those of Yon Iorns as presented in USGS Professional <br />Paper 441. Using the data in P.P. 441, an iterative process was used <br />to adjust the salinity equation such that the determined monthly <br />values would be summed to the annual values. Equations were devel- <br />oped for each station for each month and the natural salt load for <br />the entire period of record was determined. <br /> <br />Actual and Intervening Flow Stations <br /> <br />Actual flow stations in the Upper Basin are the most-upstream points <br />modeled in each tributary. The monthly values of flow and salt con- <br />tained in the hydrology data base for an actual flow station are the <br />natural flow and natural salt values described above. Since deple- <br />tions and reservoir regulation have been removed from these most- <br />upstream modeling points, the depletions and regulation must be <br />reintroduced during the modeling process. This is done at the first <br />demand point in each tributary. The first demand point contains <br />"present-level demands" which introduces all depletions, reservoir <br />regulation, exports and imports, etc., that occur upstream of the <br />most-upstream point modeled. <br /> <br />Intervening flow stations contain gains and losses in flow and salt <br />that occur along a reach of the river. A reach of the river is <br />defined as the section of river between two streamflow gauging sta- <br />tions. In the Upper Basin, monthly flow and salt values for an <br />intervening flow station (gains and losses) are computed by taking <br />the natural flow and salt values computed for the downstream station <br />and subtracting the natural flow and salt values computed for the <br />upstream station. Since natural flow and salt values are used in the <br />computation, the intervening flow and salt values are also natural. <br /> <br />~ <br />r, <br />Ii <br />I~ <br />. ~ <br /> <br />~ <br /> <br />II <br /> <br />5.3.2 Lower Basin <br /> <br />Hydrology in the Lower Basin consists primarily of gains and losses <br />in flow and salt along the Colorado River mainstem. The monthly flow <br />and salt values for both the actual flow and intervening flow sta- <br />tions are based on historical flow and salt data. Intervening flow <br />station data are then adjusted to natural conditions by taking into <br />account the effects of depletions, reservoir regulation, evaporation, <br />inflows, etc., along the reach of the river. Note that the main dif- <br />ference in computing intervening natural flow and salt values in the <br />Upper and Lower Basins is that the Upper Basin adjusts every station <br />to a natural condition with respect to the entire basin upstream of <br />the station, and then takes the difference between two stations to <br />obtain intervening values; the Lower Basin takes the difference in <br /> <br />21 <br />